Include once??

I have a file, mysql.php, that connects to the database. However, I have other files that use mysql.php that are also included in more files that also have mysql.php included.

IE:

index.php -> has mysql.php and config.php
config.php also has mysql.php

I'm getting an error when using mysql functions. Is there a way to only include once in php?

I don't understand you.

Why not just remove the include("..."); from config.php file?

Also look at these functions:
include_once();
require();
require_once();

yes you are right used this function script.